1. Field of the Invention
The present invention relates to an optical device and a rear projector.
2. Description of Related Art
There has been conventionally known a three-plate projector of front projection type in which a light beam irradiated by a light source is separated into three primary color lights of red, green and blue by a dichroic mirror, each color light is modulated by three liquid crystal panel (optical modulators) in accordance with image information, each modulated color light is combined by a color-combining optical device into a color image, and the color image is then projected on a front side of a screen in an enlarged manner through a projection lens.
On the other hand, there has been also known a rear projector in which a light beam irradiated by a light source is emitted to a liquid crystal panel (optical modulator) to be modulated in accordance with image information by the liquid crystal panel, the modulated light beam is combined by a color-combining optical device, the combined light beam is enlarged by a projection lens, and an optical path of the enlarged light beam is then converted by a reflection mirror to be guided to a rear side of a screen.
In such projectors described above, the optical modulator and a color-combining optical device are integrated as an optical device. In particular, it has been known an optical device in which the liquid crystal panel is joined and fixed on a light-incident surface of the color-combining optical device by interposing a wedge spacer or a pin spacer.
Incidentally, an optical element of the optical modulator or the like generates heat due to transmittance and absorption of the light beam, and consequently, the temperature of the optical element increases. Therefore, a cooling mechanism is typically applied thereto, in which a cooling medium such as the air is sent by a fan to directly cool the optical element itself (reference 1: JP2000-298311A, page 5, FIG. 5).
Recently, the luminance of such projectors has been increased, and accordingly, a cooling method for further efficiently cooling the optical element such as the optical modulator is required.
Though there is a conceivable method that the revolution of the fan for sending the cooling medium such as the air to enhance its cooling efficiency, this method may cause noise due to the revolution of the fan, thus not being able to reduce the noise.